We use URLs beginning with // on our site, e.g.
//youtube.com
These are perfectly valid. If you are on an http:// page then it will go to http://youtube.com. If you are on a https:// page then it will go to https://youtube.com.

The problem it seems to be giving is that sphider then tries to crawl this URL
http://wycliffe.org.uk/www.youtube.com/watch?v=TKaCKsOkznQ
wycliffe.org.uk is our site.